Automatic volume control



Jan. 15, 1935. R, D, BROWN` JR AUTOMATIC `VOLUME CONTROL Filed Dec. 6, 1929 l rent amplifier.

y volumeof la radio receiving systemsthat'strong the direct current amplifier".

Patented Jan. 15, 1935 ",'UNlTE-D AUTOMATIC vomi-im;'coN'rnony Reynolds D. Brown,` Jr.,y lliiladelphia, Pa., as* signor kto Philadelphia Storage Battery Company, Philadelphia, Pa., a corporation of Penn- 1 VSylvania Applicationnember is, 1929,'sria1No. 412,163

-f s claims. (01. 25o-2o)r app1ication,'Serial No. 405,964, led I\Tovernberv 9,1929, by D. G. McCaa and myself. It includes the features of the co-pending* application plus the double -use of a volume control amplifier either' as anaudio frequency or a radio' frequency ampli'er lin Vaddition to its use as a direct cur'- The principal object of the invention is to Aprovide a receiving system in which the output volume is maintainedk at a predeterminedrlevel in spite of any' increase ror decrease in the input carrier voltage which may be due to rvariation of vfield strength at the -antenna caused Jbyl varying v distances or variations lin power of the transmitting stationsior due:` to fading. V `.f j

Another. object is to `so control the output carrier Wavesr'are reduced toa v"predetermined level, while-carrier Waves,'fwhich "are weaker than tthat level, Will be totallyfunaffected. -'-In` other words, unless the carrienwave is present and is higher than the levelsettin'g,` the radio receiving4 system will be maintained atit'snOrmaI sensitivity. :1 f A further object is tofprovidea more sensitive controlA than has heretoforebeen-possible with systems of the prior art and Which isfobta'in'ed by fderivinga `direct current `voltage vfromy the system, 'amplifying 'this'fvoltage' 'and then using the amplied voltage to bias' the grid orfgrids ofone or more `tubesl ofY thesystem.

Another object of the-invention is'toY provide ab sensitive automatic I volumek A' control which,

` When'incorporatefl` `with a receivingsysterni will,

function `without.producing howls due to the settingup :of local oscillations orf'the feeding' baci; of Vundesirable oscillations frorni'the ysyste'xrr'into:

'A stili further object` of" the invention'11s.L to' provide a direct current amplifier for amplifying the derived vdirectl current `voltageswhich may be used additionally as an amplifier" of. eitherv radio or audio frequency currents.`

,. The biasing voltage may be yderivedfrom the outputoI-gthe detector tube, as 'shown` in, one' modification or it maybe derivedfrorn any. tubel other than the detector, as may be desired.

, Some ofthe featureslof. thevoltage control ofv the present inventionv which distinguish'it fromthe prior art are:A y j (1) The provision of a vspecial radio frequency lter iny the grid Acircuitin thetube or tubes Which are automatically biasedand theprovision ofv 'other' lters in `the systemV which make for the f diievrence bet-Ween satisfactory operation "of the system -and a system which would 'set' up undue howls caused by local oscillations!k being generated. l f f (2) The use of a high impedanceA primary coil STATiss-w PA-TENT; OFFICE?? in the outputcircuit of the'automatically biased s (3) Theuse-of a -direct'lcurrent amplifier't'o increase the eiect 'of thebiasing voltage derived from the system; i' f (4) The provision yof an automaticfbiasing means on the detector k-itselff.4 (5)" The use -of'a level-'adjusting resistance begtween rthe automatic biasing lmeans in the plate circuit Vof' the'detector and the grid orfgrids bf the `direct current amplifier instead'of using a voltage .divider inthe audio output circuit; 'ff n z A clear understanding of the description, and operation ofy 'the system will be `had from the drawing; in 4vvhich the single figure is'avvirilng ydiagram of ahradioreceiving vsystem with the modications and additional apparatus required to carry`out my invention'withthe use ofv ag'rifd bias detector.l s -f f vl'Referrin'g to'li'g. 1,",the`vacuum` tubes'Vi and V2 vare radio lfrequencyV arnplifyin'g'tubes which are connected in cascade by meansfof'transform"A eruTifancl then antenna circuitiscoupled-fto the tube V1 byv means' of.v the transformer '12* lollt'mv-4 ing the tube-V2 is a detector tube -Va' 'of thegrid bias .typei which is coupledto-tube V2 by inearisv of? transfrmer! T2 and has` its output coupled to the. tubes V4 and V5' byrneans of transformen T3. Tubes .V4 andV5 are coupled to anou'tputlcircuit by yrneans' oftransformer T4. All of 'the tubes [of thsystem shown are of the heater-,type'land they heating currentl is derived v'f-iornr an'alternatin'ig" currentsource,j but it'is obvious that the fiile.;

ment typeof tubes 'may be used. Tub-"Vzfmay the output of the detector V3. The tuned circuits of tubes V1, V2 and V3 are adjusted by the variable condensers VC which are arranged to 1 be adjusted simultaneously. In order to prevent 'self-oscillation of this system, the vtube V1 is neutralized by means of condenser Ca and in order to prevent undesirable oscillations from being fed from .the output circuits offtubes V4 and-'V5 into the'direct current amplifier, and

into grid-cathode circuits of tubesV1 and V2, spef4 cial filters are provided comprising radio fre plate circuit of detector tube V3 are a, radioiree.

quency choke RFC, a radio frequencybypass .condenser Cv and .anaudio frequency by-pass condenser Cs. The special-,filters and allfof :the various, by-passes-1addV to the` satisfactory operation .of the system.l The detector tube VsA is-pro vided with ari-.automatic biasing means comprisingv resistance R and; condenser Cconnected in parallelwith. each other` and placedY in series Witl'ir the plate .cathode circuit .oflthe tube. The point Whichis the lower end of the secondary S may be `connected to ground, as indica-ted in .the diagram, .or .it may be connected to the -upper terminal. .of theVv time circuit (RC) or toany other point of.appropriatedirect current potential. The positive end of the RC circuiitfwhichis indicated `in theY drawing'.as` the upper end, is connected tolonelendnof .appotentiometer r1, The tap y of potentiometer r1 is connected to the centertap of the secondary iSaf of, the transformer Ta, the terminals rif-which .are connectedto the :grids .of tubes Viaud. V5, Thefothei terminal nof .potentiometer r1 is` connected toa posi* tive potential of 20 volts. Theca-thodes of; tubes V4 andl Vearerconnectedto a pointe which-may be cornsiected to` azpositii/e potentie-L 0f.."70 volts', The .primary vP4, which, .connectsA the plates., of tubes V4 and -ispz'ovidedi-with a: center *294D Whichis connectedfthlioughanother time :cire

Wilt BTC t :a Source'ofsdirect .current patenting!l ofsuch magnituvsle` as requiredbyfthe anodesfof.

the .tubes VV4 and V5.4 The upper terminal :of: the

time circuit RC', which is designated as being negative, is connectedback tothe grid circuit opt tube V1;y fand-through the resistance `nl ato resistance vmand-the Agrid circnitxof tube V2... .The resistances n' and rs` are;providedV to rproduce Vdifferent .degrees yof automatic-.grid bias: on .the tubes V1 andiVz. The ratio of resistancereto 1.15

of automatic bias on thee grid of tube V1 isfbur times. that ofthe bias-on,tubev V2; The plates oi thetubeslVn ,V2 anti-V3` are supplied". with, ape propriete positive potentials;w .as indicated; f The potentiometer r1 isv used ytoadjusl; the carrier. output level to any predetermined valueland whenits variabletap ismoved tofthe upper "endf une primary P21 the 'output circuit, of unev ylower grid bias'.

tube V2 comprises, for example, vsixty turns instead of the usual fteen turns and provides a high impedance in the output circuit to match the internal impedance of the tube V2.v By providing a highimpedance primary of the transformer T2, maximum amplification is obtained with a higher bias voltage on the grid of tube V2 than when a standard transformar Y ed in which maximum amplification occursa "a much It is, therefore, apparent that lwith a high impedance primary, a lower negative volilge` .isrequired on the grid of tube V2 to cut off the signal.

The .opera-tion 4of the systemisas follows:- 'whenjtherek is no vcarrier present, no current flows"in T1 because `the upper terminal of cir- -cuit RC is at a positive potential of 20 volts and y:the other' `end of r1 .is connected to a positive potential of 20 volts. Whenfa carrier is present andthe carrier voltage increases, the plate current in the detector tube increases and the upper .terminal-,of the RC circuit becomesfmore positive or less negative, thereby making thel grid ofthe detector more .negative and the grids of @the push-,pull tubesV Vl and V5 less negative and allowing. more plate current to flow .through .the circuit` RC and causing an increased negative voltage to be impressed on the grids of tubes V1 and; Vzvtfrom the upper Vterminal RC'.; lhe adjustment of the carrier level by meansfof the potentiometer r1 has no,V direct Aeffect on the audio frequency signal level. that when the :carrier voltage increasesjt mediatelyk produces a direct,currentA- yoltage across. the points 11, .z which isfimpressedon the grids of tubes Vi and V5 where; itis amplied and causes an increasedcurrent to 110W ,th-rough circuit B2C', whereby an` increased potential drop .i-sproduced and `is* applied tothe gridswof the vtubesVi and V2 which. causes areductionof amplication in these tubes and restoresfthe carrier output to the level for whichthe-sys-4 It WillA be; Seen" tubes. V 4 :and V5v act, in :parallelfrelation-.asfrdirect current ampliersnsince-the grids are aitthe aunev potentials: simultaneously Aand their: outputs,` f alie connected so that. the plate currentszifrom :the

twetubes are` .additive in;` .their aect. andthe cir'- cuit RCj., jHowevemfpr audio frequency 'signal' currents, the tubes V4 and V5 act in puShenulL rela-tion since,- the of' one tube iszpositive, while :thexgrid :of thelother' tube is negative and viceversa.. f

WhentheV tubes normal value for pushf-pnll action, `thererfis,

no` change in the V'total plate curr-entf the tubes due to audiovireguencygcurrentsand, there, fore, .there `is no 1f eect on I'.-C y .except that ,due

tothe bias. .voltage .derived from the circuit. RC.

While Ifhav .shown only- :torm of .embodi- `ment of my invention, or the purposebfQde' sc'ript'ionv and illustration of 'its principlesfof construction and operation, it is apparentftlat various changes 4and modii'lcations may. bemade therein'without departing from the` scopeo'f the' invention.,k I desire, therefore, that only such limitatimsv shalli'be imposedl thereon as'are inl- ,dicatedin' theappended claims or, asV are' ,de-- .mandedibythe prior'art. f* i v n ing."a;*plurali`ty of carrier frequency amplifying tubes,` fa,- detector and audio. frequency' ampli1-'4 fying .tubes lin: push-pull" relation', .themethodi of: .automaticallywcontrolling the carrier output level which comprises deriving a un-directional voltage from the plate circuit of said push-pull tubes, the value of said voltage depending on the carrier voltage, and causing said derived voltage to affect one or more of the carrier frequency amplifying tubes, thereby reducing the efficiency of the system in accordance With the carrier amplitude.

2. In a carrier wave receiving system including a plurality of vacuum tubes, one of said tubes having a higher amplification factor than another of said tubes, the method of'automatically controlling the output level of said system comprising deriving a uni-directional current from said system, passing said current through a divided resistor to produce a plurality of voltages, and applying one of said voltages to the grid of the lower amplification tube and the lesser of said voltages to the grid of the higher amplification tube, whereby their efficiencies are modied to substantially the same extent.

3. In a carrier Wave receiving system comprising a plurality of carrier frequency amplifying tubes, 'a detector and audio frequency amplifying tubes in push-pull relation, the method of automatically controlling the signal output level which comprises deriving a uni-directional voltage from the plate circuit of said push-pull tubes, the value of said voltage depending on the signal voltage, and causing said derived voltage to aect one or more of the carrier frequency amplifying tubes, thereby reducing the elliciency of the system in accordance with the signal amplitude.

4. In a carrier wave receiving system comprising a plurality of carrier frequency amplifying tubes, a detector, and audio frequency amplifying tubes in push-pull relation, means for automatically controlling the signal output level of the system comprising means for deriving a uni-directional voltage from the plate circuit of said push-p tubes, the value of said voltage depending upon the signal voltage, and

means for causing said derived voltage to effect one or more of the carrier frequency amplifying tubes, thereby reducing the efficiency of the system in accordance with the signal amplitude.

6. In a carrier Wave receiving system comprisautomatically controlling the signal output level which comprises deriving a uni-directional voltage from the circuit of the detector, the value of said voltage depending on the signal voltage, applying said voltage in parallel to the input of said push-pull tubes, deriving a second unidirectional voltage from the plate circuit of saidA push-pull tubes, and causing said second unidirectional voltage to effect one or more of the carrier frequency amplifying tubes, thereby reducing the efciency of the system in accordance with the signal amplitude.

6. In a carirer Wave receiving system comprising a plurality of carrier frequency amplifying tubes, a detector, and audio frequency amplifying tubes in push-pull relation, means for automatically controlling the signal output, level,

comprising means for deriving a uni-directional' voltage from the circuit of the detector, the value of said voltage depending on the signal voltage, means for applying said uni-directional, voltage in parallel to the input of said pushpull tubes, means for deriving a second unidirectional voltage from the plate circuit of said push-pull tubes, and means for causing said, 

